Čerenkov counting and liquid scintillation counting of cl · 89 sr 0.7630 0.59285 0.5909 -0.33...

Physikalisch-Technische Bundesanstalt

erenkov counting and

liquid scintillation counting of 36Cl

Karsten Kossert, Ole Nhle

Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany

and Agustn Grau Carles

Instituto de Fsica Fundamental (CSIC), Madrid, Spain

LSC 2010, Advances in Liquid Scintillation Spectrometry,

Paris, 6-10 September 2010

Kossert, Grau Carles, Nhle erenkov and LS counting of 36Cl

Motivation

The application of a new TDCR-erenkov technique for the

activity determination of 36Cl revealed discrepancies with liquid

scintillation counting.

This discrepancy indicates errors in the computation of the beta

emission spectrum.


The TDCR-erenkov method


BasicsCharged particles produce erenkov light when traveling in a

transparent dielectric medium with v>c/n

Electrons: m0 = 511 keV/c2 v/c=>1/n

At threshold: =1/n

in keV

21

1/ 511 1

=

+ E

2

th1

1511 1

(1 )

= n

E


Basics

in keV

0

100

200

300

400

500

600

700

1,0 1,2 1,4 1,6 1,8 2,0

refractive index n

Eth

in

ke

V

2

th1

1511 1

(1 )

= n

E

water:

n = 1.333

Eth = 261.6 keV


BasicsCherenkov light emission has a directional character (not isotropic)

1cos =

n

water:

n = 1.333

max = 41.40

5

10

15

20

25

30

35

40

0 500 1000 1500 2000 2500 3000 3500

Energy in keV

i

n


Basics

According to the Frank and Tamm theory the number of photons

per unit path is given by

- FS is the fine structure constant- n is the refractive index of the medium (here non-dispersive)

- =v/c- 1 and 2 are the lower and upper limit of the wavelength region

FS 2 2

1 2

d 1 1 12 1

d

=

k

x n


A new TDCR-Cherenkov technique

Number of photons is computed by numerical (Romberg)

integration

where

The electron stopping powers dE/dX

are taken from the ESTAR database

(NIST)

FS 2 2

1 2

d 1 1 12 1

d

=

k

x n

th

d 1( ) d

d d / d=

E

E

kk E E

x E X

0 500 1000 1500 2000 2500 3000 3500 4000

in keVE

0

100

200

300

400

500

600

700

(

)k

E



- Assumption: The number of created photoelectrons follows the

Poisson statistics, i.e. we can apply a free parameter model.

( )( )( )0

31 2

th

( )( ) ( )

T ( ) 1 e 1 e 1 e d =

E

qk Eqk E qk E

E

N E E

( )( )

( )( ) ( )( )

( )( )( )

0

1 2

th

3 31 2

31 2

( ) ( )

D

( ) ( )( ) ( )

( )( ) ( )

( ) 1 e 1 e

1 e 1 e 1 e 1 e

2 1 e 1 e 1 e d

=

+ +

E

qk E qk E

E

qk E qk Eqk E qk E

qk Eqk E qk E

N E

E



The anisotropy is described with only one parameter :

For =1/3 the formulas are similar to the TDCR formulas for LS.

( )( )( )0

31 2

th

( ) )( ) ( )

T ( ) 1 e 1 e 1 e d =

E

qk Eqk E qk E

E

N E E

( )( )

( )( ) ( )( )

( )( )( )

0

1 2

th

3 31 2

31 2

( ) ( )

D

( ) ( )( ) ( )

( ) )( ) ( )

( ) 1 e 1 e

1 e 1 e 1 e 1 e

2 1 e 1 e 1 e d

=

+ +

E

qk E qk E

E

qk E qk Eqk E qk E

qk Eqk E qk E

N E

E

1 = 23

(1 )2

= 33

1 (1 )2

=



-1.080.1327-2.530.13070.134100.3830204Tl

0.290.88340.230.88290.880830.9277106Rh

0.180.77100.030.76990.769660.874590Y

0.030.5930-0.330.59090.592850.763089Sr

0.070.6878-0.210.68580.687250.793132P

(E ) (x=0.655)(=0.41)

(D,calc-D,exp)/ D,exp in %D,calc

(D,calc-D,exp)/ D,exp in %D,calcD,expTDCRNuclide

K. Kossert, Applied Radiation and Isotopes 68 (2010) 1116-1120



The new method works excellent for several beta emitters,

but

calculations for 36Cl yield discrepancies up to 10%.



The method was extended and

improved:

- Wavelength-dependent PMT response

curves are taken into account

- Wavelength-dependent refractive

index (dispersion) is taken into

account

- PMT asymmetries are taken into

account (3 free parameters and

Downhill Simplex algorithm)

But: discrepancies for 36Cl remained.

100 200 300 400 500 600 700

wavelength in nm

0.01

0.1

1

10

quan

tum

eff

icie

ncy

in %

HAMAMATSU R331-05, 2"HAMAMATSU R331, 2"BURLE 8850, 2"

200 300 400 500 600 700

in nm

1.32

1.33

1.34

1.35

1.36

1.37

1.38

1.39

1.4

1.41

1.42

1.43

1.44

1.45

1.46

1.47

1.48

refr

acti

ve

index

of

wat

er

Fit used in this workEq. 1 from Thormahlen et al.


36Cl beta spectrum

Beta transition is 2nd

forbidden (non-unique) Decay scheme from DDEP:www.nucleide.org

N(W)dW = AW(W2-1)1/2(W0-W)2F(Z,W) C(W) dW

A=g2/23); W is the total electron energy in units of the rest mass; W0 is the maximum

value for W; F(Z,W) is the Fermi function taking into account distortion due to nuclear

charge; C(W) is the shape factor function


36Cl beta spectrum

Determination of 36Cl beta spectrum:

Reich and Schpferling, 1974 4-Si(Li) spectrometer

Sadler and Behrens, 1993 theory

Grau Malonda and Grau Carles, 1998 shape-factor derived from

Sadler and Behrens

Grau Carles, 2005 LS cutoff energy yield method

Rotzinger et al., 2008 cryogenic magnetic calorimeters

This work derived from exp. data of

Rotzinger et al.


36Cl beta spectrum

0 100 200 300 400 500 600 700

Energy in keV

0

0.01

0.02

0.03

pro

bab

ilit

y i

n a

rbit

rary

un

its

Fit of exp. data from Rotzinger et al. (2008)

Grau Carles (2005)

Grau Malonda and Grau Carles (1998)

36Cl shape-factor function as determined in this work using

experimental data: C(W)=1-1.326W+0.6328W2


LS sample composition: 15 mL Ultima GoldTM + 1 mL water, glass

vials, quenching agent: Nitromethane

erenkov samples: 12 mL HCl (1 mol/L) in PE vials

Preparation by difference weighing of a pycnometer with traceable

balances

Experimental details


Reference activity was determined by means of LS counting using

CIEMAT/NIST efficiency tracing and TDCR.

Efficiency was computed with MICELLE2 using

kB = 0.0075 cm/MeV.

LS measurements

Counters:

- Wallac 1414

- TriCarb 2800

- TDCR system of PTB


For TDCR, efficiency reduction

is necessary.

Results:

CN: 9.029(27) kBqg-1

TDCR: 9.047(27) kBqg-1

LS measurements

-1.00

-0.75

-0.50

-0.25

0.00

0.25

0.50

0.75

1.00

0.225 0.250 0.275 0.300 0.325 0.350 0.375 0.400

tracer

(ai-a

mean)/

am

ean i

n %

a)

-1.00

-0.75

-0.50

-0.25

0.00

0.25

0.50

0.75

1.00

0.275 0.300 0.325 0.350 0.375 0.400 0.425 0.450 0.475

tracer

(ai-a

mean)/

am

ean i

n %

b)

-1.00

-0.75

-0.50

-0.25

0.00

0.25

0.50

0.75

1.00

0.982 0.983 0.984 0.985 0.986 0.987 0.988 0.989 0.990

TDCR

(ai-a

mean)/

am

ean i

n %

c)


Standard uncertainty components for LS counting

LS measurements

0.290.30Square root of the sum of quadratic components

0.010.01Decay correction

0.100.10PMT asymmetry

--0.02Quenching indicator (SQP(E), tSIE)

0.010.01Ionization quenching

0.250.25Decay data (endpoint energy and beta shape-factor function)

0.010.013H activity/TDCR value and fit

0.050.05Radionuclide impurities (none detected)

0.050.05Adsorption

0.010.01Time of measurements (starting time and duration (life-time))

0.030.03Background

0.030.10Dead time

0.020.02Weighing

0.010.02Standard deviation of the mean (samples:5 (4 for TDCR);

repetition per sample for each counter: 8)

TDCRCIEMAT/

NIST

u(a)/a in %

Component


Alburger et al. (1986) measured 36Cl and 32Si/32P with an end-

window gas-flow proportional counter.

Seasonal fluctuations of the decay-corrected counting rates in the

order of 310-3 were observed with a maximum in February and

minimum in August.

Jenkins et al. (2009) developed a contentious explanation:

A correlation between the decay constant and the Earth-Sun distance

(corresponds to a change of the solar neutrino flux).

Our LS-TDCR measurements were started in Dec. 2009 and some

repetitions were made in summer 2010 to detect potential seasonal

effects.

Seasonal effects?


Deviation between the Dec. and the July measurements: about (2.32.5)10-4.

We can exclude seasonal variations of the decay rate of 36Cl in the stated

order. The measurements will be continued.

Seasonal effects?

-0.0233(246)9.04939.04989.0472Mean

-0.0169(259)9.0502(4)9.0482(25)9.0486(23)5

-0.0238(205)9.0483(7)9.0498(28)9.0461(17)4

-0.0253(170)9.0481(7)9.0470(25)9.0459(14)3

-0.0272(351)9.0507(14)9.0543(27)9.0482(29)2

Deviation (a1-

a3)/a

1in %

a3

in kBqg-1a2

in kBqg-1a1

in kBqg-1Sample

No.

Comparison

(Dec. July)

6-12 July 2010

measurement

14-16 June

2010

measurement

10-14 Dec.

2009

measurement


Reasonable agreement is obtained with the new shape-factor function.

Theoretical prediction from Sadler and Behrens (1993) can be ruled out.

erenkov counting results of 36Cl

D, , calc

D, , calc

D, , calc

-3.840.2010-6.320.2036-6.490.2032Grau Carles

(2005)

1-1.167W

+0.884W2

10.010.23917.350.23337.190.2330

Grau Malonda

and Grau Carles

(1998)

1-1.875W

+1.375W2

0.160.2177-2.260.2124-2.400.2121

This work (with

exp. data from

Rotzinger et al.

(2008))

1-1.326W

+0.6328W2

x in %x in %x in %

=1.0, n=1.341, dispersion for

water

=1.07, n=1.331, dispersion for

water

=1.11, n=1.341, no dispersion

ReferenceShape factor

C(W)

D, , calc D, , exp D, , exp( ) /x =


Summary

A new shape-factor function was derived for 36Cl.

The results of LS measurements and TDCR-erenkov counting are in

reasonable agreement when using the new shape-factor function.

This confirms the results from Rotzinger et al. (2008).

From our LS-TDCR data we find no evidence for a correlation of the

decay rate and the Earth-Sun distance.


Outlook

Potential application of the new TDCR-erenkov method:

- measurement of radionuclides for nuclear medicine (e.g. 32P, 89Sr, 90Y)

- measurements in environmental radioactivity (e.g. 210Pb, Sr isotopes)

- due to the large sensitivity on shape-factors the method can provide

useful information on beta spectra (as shown for 36Cl)

- preliminary tests indicate that the method can also be applied

with the new Hidex-TDCR counter

- further effects must be investigated, e.g. bremsstrahlung and direct

interaction of electrons with PMTs (see e.g., full MC approach

from Bobin et al. (2010))

The recent extensions and improvements as well as a computer

program will be published soon.


Thank you for your attention

Čerenkov counting and liquid scintillation counting of cl · 89 sr 0.7630 0.59285 0.5909 -0.33...

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